Insulating cartridge

ABSTRACT

The invention relates to an insulating cartridge for use as part of a pipe jacket insulation, comprising a substantially closed sheet metal casing ( 5 ) which completely encloses an insulating material filling ( 7 ). The insulating cartridge ( 2 ) according to the invention is characterized in that the insulating material filling ( 7 ) comprises a silicate aerogel.

The invention relates to an insulating cartridge as part of a jacket of devices of a steam generator which are under media pressure, for example as pipe casing insulation, with an essentially closed sheet metal housing which completely encloses an insulating material filling.

Such an insulating cartridge is often used for the thermal insulation of pipe lines at steam generators.

The known insulating cartridges are sheet metal cartridges which are in the form of half shells and are filled with mineral wool, glass fiber wool or similar insulating materials. These are described, for example, in DE 29 23 094 A. In the cold insulation and thermal insulation of pipe lines, it is customary to provide insulating materials with a jacket which protects the insulating material against climatic conditions and mechanical damage. The jacket of the insulation is frequently carried out by sheeting the insulating material, for example with sheet zinc. In some applications such as, for example, in coolant circuits of nuclear power stations it has proved appropriate to use closed insulating cartridges which completely enclose the insulating material. In particular, the sheet metal housing of the insulating cartridges is intended to afford sufficient protection against mechanical damage to the insulating material. However, in accidents involving the loss of coolant in nuclear power stations, it may nevertheless happen that the metal cartridge is destroyed and the insulating material contained in it escapes. For example, the situation could arise where the leakage jet from a coolant line causes an insulating cartridge to be broken off and destroyed. Insulating cartridges of the type described above are provided, for example, for lines with a diameter of up to about 800 mm and an internal pressure of 160 bar at a media temperature of about 300° C. It can easily be imagined that the leakage jet from such a line may introduce relatively high mechanical forces into the insulating cartridge.

In this case, it could happen in theory that the sheet metal housing of an insulating cartridge breaks and the insulating material is flushed out by the leakage jet of the coolant. The washed-out insulating material could block the intake screens of the pumps provided in the reactor sump, with the result that it becomes difficult to bring the accident under control.

It became apparent that there was a fundamental problem in retaining or keeping out fibrous insulating materials by means of screens. Laboratory tests showed that the fiber material, on the one hand, is difficult to retain by means of relatively fine-meshed screens and, on the other hand, generates high pressure losses across the screens during its accretion. This may lead to the failure of the screens.

The object on which the invention is based, therefore, is to improve in this respect an insulating cartridge of the type initially mentioned.

The object on which the invention is based is achieved by means of an insulating cartridge as part of a jacket of devices of a steam generator which are under media pressure, for example as pipe casing insulation, with an essentially closed sheet metal housing which completely encloses an insulating material filling, the insulating cartridge being distinguished in that the insulating material filling comprises an aerogel. Aerogel is to be understood generally and in the context of the invention as meaning highly porous solids in which up to 95% of the volume is composed of pores. Using this material as filling material for an insulating cartridge has the advantage that, for example, material emerging from the insulating cartridge can be kept out of a water circuit more easily by virtue of its physical properties.

Preferably, the insulating material filling provided is an inorganic aerogel which is non-wettable, is floatable and is incombustible. An insulating cartridge in which the insulating material filling comprises a silicate aerogel has proved to be especially advantageous. Such silicate aerogels may have, for example, a pore diameter of about 20 nm with a porosity of >90%. The density of the material may amount to between 90 and 100 kg/m³. Thermal conductivity may amount, for example, to about 0.018 W/m·K at 25° C. Such material may have an internal surface area of about 600 to 800 m²/g. The material is therefore predominently suitable as insulating material for the purposes described above.

For example, what may be used as a suitable silicate aerogel is material bearing the commercial designation “Nanogel” which is sold by the company CABOT Corporation.

In an expedient variant of the insulating cartridge according to the invention, there is provision for the insulating material filling to comprise an aerogel as a granulate, preferably with a mean grain size of 0 to 4 mm. Such a granulate possesses, in particular, handling benefits. It can be decanted into corresponding filling orifices of sheet metal cartridges. The insulating cartridges can be filled with the highest possible packing density.

Alternatively, the insulating material filling may comprise at least one aerogel molding. Such a molding could be adapted to the configuration of the preferably dimensionally stable sheet metal housing. The sheet metal housing of the insulating cartridges may be composed, for example, of austenitic steel. In an especially preferred variant of the insulating cartridge according to the invention, there is provision for the aerogel to be non-translucent. A correspondingly treated aerogel may be used for this purpose. The advantage of this is that the infrared reflectivity of the sealing material used is increased and therefore the insulating action is improved.

For this purpose, for example, the insulating material filling may comprise graphite powder and/or metal oxide powder. The powder may, for example, be in a homogeneous mixture with an aerogel granulate. For example, the insulating material filling may comprise aerogel and graphite powder and/or metal oxide powder in a homogeneous mixture, the fraction of graphite powder and/or metal oxide powder being between 1.5 and 4.5 ma %.

Expediently the insulating cartridge according to the invention has an approximately C-shaped cross section and is provided with fastening means by which insulating cartridges designed complementarily to one another can be assembled to form an essentially closed pipe casing.

Within the scope of the invention, however, the insulating cartridge may be adapted to any desired contour of a media-carrying device to be insulated.

The invention is explained below by means of an exemplary embodiment illustrated in the drawings in which:

FIG. 1 shows a diagrammatic view of a pipe line which is clad with insulating cartridges according to the invention,

FIG. 2 shows a top view along the arrows II-II in FIG. 1,

FIG. 3 shows a longitudinal section along the arrows III-III in FIG. 2,

FIG. 4 shows an exploded view of an alternative embodiment of the insulating cartridge according to the invention, and

FIG. 5 shows the insulating cartridge from FIG. 5 in the assembled state.

FIG. 1 shows a pipe line portion 1 of a high-temperature pipe line carrying a medium which is under pressure. The pipe line portion 1 is clad with insulating cartridges 2 according to the invention, the insulating cartridges 2 having in each case a C-shaped cross-sectional profile, and two mutually complementary insulating cartridges 2 being assembled in each case with fastening means 3 to form a closed tubular insulating jacket 4. What may be considered as fastening means are, for example, known shackle-type toggle fastenings. Each insulating cartridge 2 is composed of a riveted or welded sheet metal housing 5, preferably made from austenitic sheet steel. The sheet metal housing is closed over the entire circumference and on the end faces 6 and is provided with an insulating material filling 7. In the variant of the insulating cartridges 2 which is shown in FIGS. 1 to 3, these comprise an insulating material filling in the form of a granulate of a silicate aerogel. Here, this is a granulate with a mean grain size of 0 to 4 mm, comprising trimethylsilyloxy-modified silica gel as the main component. This has a porosity of >90%, a pore diameter of about 20 nm, a bulk density of between 90 and 100 kg/m³ and a thermal conductivity of about 0.18 W/m·K at 25° C. The specific surface area amounts to between 600 and 800 m²/g. The aerogel is incombustible and non-wettable and floatable.

The granulate is introduced into the insulating cartridges through orifices 8 provided on the end faces of the latter. The orifices 8 are subsequently closed by means of covers 9. The covers 9 may be welded, screwed or riveted.

FIGS. 4 and 5 show a further exemplary embodiment of the insulating cartridge 2 according to the invention. The insulating material filling 7 is formed as a molding 10, the configuration of which is adapted to the configuration of the dimensionally stable sheet metal housing 5.

The molding 10 is inserted with a fit into the sheet metal housing 5, the end face 6 of which is closed by means of a correspondingly formed cover 9.

The areogel, either in the form of the granulate or of the molding 10, is improved in terms of its infrared reflectivity, that is to say its insulating properties with regard to thermal radiation, by means of coloring. For example, dusting of the molding 10 with graphite powder and/or metal oxide powder may be considered. The granulate may be mixed with graphite powder and/or metal oxide powder, the graphite powder and/or metal oxide powder having a fraction of 1 to 4 ma % in the mixture.

LIST OF REFERENCE SYMBOLS

-   1 Pipe line portion -   2 Insulating cartridge -   3 Fastening means -   4 Insulating jacket -   5 Sheet metal housing -   6 End faces -   7 Insulating material filling -   8 Orifices -   9 Cover -   10 Molding 

1. An insulating cartridge as part of a jacket of devices of a steam generator which are under media pressure, for example as pipe casing insulation, with an essentially closed sheet metal housing which completely encloses an insulating material filling, characterized in that the insulating material filling comprises an aerogel.
 2. The insulating cartridge as claimed in claim 1, characterized in that the insulating material filling comprises an inorganic areogel.
 3. The insulating cartridge as claimed in claim 1, characterized in that the insulating material filling comprises a silicate aerogel.
 4. The insulating cartridge as claimed in claim 1, characterized in that the insulating material filling comprises an aerogel as a granulate, preferably with a mean grain size of 0 to 4 mm.
 5. The insulating cartridge as claimed in claim 1, characterized in that the insulating material filling comprises at least one aerogel molding.
 6. The insulating cartridge as claimed in claim 5, characterized in that the molding is adapted to the configuration of the preferably dimensionally stable sheet metal housing.
 7. The insulating cartridge as claimed in claim 1, characterized in that the aerogel has increased infrared reflectivity.
 8. The insulating cartridge as claimed in claim 7, characterized in that the insulating material filling comprises graphite powder and/or metal oxide powder.
 9. The insulating cartridge as claimed in claim 7, characterized in that the insulating material filling comprises aerogel and graphite power and/or metal oxide powder in a homogeneous mixture, the fraction of graphite powder and/or metal oxide powder being between 1.5 and 4.5 ma %.
 10. The insulating cartridge as claimed in claim 1, characterized in that it has an approximately C-shaped cross section and is provided with fastening means by which insulating cartridges designed complementarily to one another can be assembled to form an essentially closed pipe casing. 